This invention relates generally to air bag modules for installation in passenger vehicle and, more particularly, to an inflatable air bag module having means for augmenting gas delivered from an inflator to an air bag.
Many passenger vehicles manufactured today are equipped with air bags for the front seat passenger. This air bag is part of an air bag module which includes an inflator attached to the air bag and a container for housing the air bag and the inflator.
This air bag module is located in a recess in the vehicle instrument panel for deployment of the air bag through an instrument panel opening which is normally closed by a cover door. The inflator is actuated by a signal received from a vehicle deceleration sensor to discharge pressure gas through discharge ports into the air bag interior. Upon inflation, the air bag forces the cover door open and deploys into the passenger compartment rearwardly of the instrument panel.
Inflators utilized in this type of installation generally have a cylindrical outer casing. The container has a U-shaped bottom portion, comprising part-cylindrical bottom and side walls which house the inflator. The container has a top opening that connects to the air bag interior. The inflators are conventionally assembled to the container by assuring proper orientation and then applying fasteners, such as nuts and bolts.
Various types of cylindrical inflators are used in this arrangement. In one, the canister is mounted on the bottom wall and gas discharge ports are located on only the top side of the inflator facing the air bag opening. This type is known as a directional inflator and is characterized by having a downward resultant reaction force on the module when actuated.
Another type of inflator features gas discharge ports located on diametrically-opposite sides of the casing. This arrangement of the discharge ports makes the inflator thrust neutral, since the gas discharge forces on opposite sides of the inflator cancel, with no resultant forces on the module.
With either type of inflator, it is important to quickly inflate the air bag to provide occupant cushioning. Quicker filling can be accomplished by using an inflator which generates more gas quickly. However, this involves use of a larger and heavier inflator. Another solution is to aspirate ambient air during air bag inflation to supplement the inflator-generated gas with air to increase output to more quickly fully inflate the air bag.
An inflator arrangement for increasing gas output is illustrated in U.S. Pat. No. 4,846,368--Goetz in which a directed thrust inflator is used in an inflator container, or reaction canister, having holes in its side walls. These holes are normally covered by flexible flaps. Upon actuation of the inflator, the discharge of pressure gas from the canister causes a pressure reduction around the sides of the canister, due to the Bernoulli effect. This resultant pressure imbalance forces the flaps inwardly to aspirate ambient air to the canister. This supplemental ambient air augments the gas discharged by the inflator, increasing the total gas volume available to inflate the deploying air bag.
A similar arrangement is shown in U.S. Pat. No. 4,928,991--Thorn which also utilizes directed thrust gas generation and side wall aspiration holes covered by a flap. In both of these patents, an increase in air bag pressure causes the flaps to close. This requires other means of accommodating pressure increases.
As gas pressure rises upon occupant engagement in the Goetz arrangement, these flexible flaps will close to prevent exhaust of gas through these holes. To reduce gas pressure, auxiliary rear vent holes are provided. These are covered with a foil that ruptures to vent the gas to reduce air bag pressure.
It would be desirable to provide a simplified air bag module which uses a directional inflator that enables the augmentation of discharge gas by aspiration of ambient air.
It would also be desirable to provide an air bag module of simplified construction which provides relief for excessive air bag pressure.
It would be further desirable to provide an air bag module which supplies initial high air bag pressure to initiate air bag breakout immediately followed by a momentary pressure reduction to reduce the breakout forces, followed by aspiration to augment discharge gas during air bag deployment.
It would be yet further desirable to provide an inflator mounting which is quick, assures proper inflator orientation, and eliminates separate fasteners.